Silicon quantum device structures defined by metallic structures

ABSTRACT

A silicon-based quantum device is provided. The device comprises: a first metallic structure ( 501 ); a second metallic structure ( 502 ) laterally separated from the first metallic structure; and an L-shaped elongate channel ( 520 ) defined by the separation between the first and second metallic structures; wherein the elongate channel has a vertex ( 505 ) connecting two elongate parts of the elongate channel. The device further comprises: a third metallic structure ( 518 ), mediator gate, positioned in the elongate channel; a fourth metallic structure ( 531 ) forming a first barrier gate, arranged at a first end of the third metallic structure; and a fifth metallic structure ( 532 ) forming a second barrier gate arranged at a second end of the third metallic structure. The first, second, third, fourth and fifth metallic structures are configured for connection to first, second, third, fourth and fifth electric potentials respectively. The first, second, fourth and fifth electric potentials are controllable to define an electrical potential well to confine quantum charge carriers in an elongate quantum dot beneath the elongate channel. The fourth and fifth electric potentials and the position of the fourth and fifth metallic structures define first and second ends of the elongate channel respectively. The width of the electrical potential well is defined by the position of the first and second metallic structures and their corresponding electric potentials; and the length of the electrical potential well is defined by the position of the fourth and fifth metallic structures and their corresponding electric potentials. The third electric potential is controllable to adjust quantum charge carrier energy levels in the electrical potential well.

FIELD OF THE INVENTION

The present invention relates to a silicon-based quantum device forquantum computation.

BACKGROUND TO THE INVENTION

Quantum computations typically require large numbers of qubits. In thenear-term intermediate-scale quantum computing, or NISQ, era, quantumcomputational processes may use 50-100 qubits. Qubits are typicallyarranged in dense arrays within a quantum device so as to minimise thenecessary processor size.

It is desirable to be able to address each qubit with an individualelectrode to allow an experimentalist to manipulate the qubits withinthe device. However, the routing of electrodes used to address thequbits typically requires space comparable to or larger than the spaceoccupied by the qubits alone, within the qubit array or qubit lattice.For planar qubit lattice layouts, the qubits therefore need to be spacedout in order to have enough space to pattern the electrodes.

It has been suggested that routing can be performed vertically, using aconductive via which extends perpendicular to the surface of the device.However, this is a complex method with a large number of processingsteps and a high failure rate.

It is desirable to create a scalable device structure for use in quantumcomputing.

SUMMARY OF THE INVENTION

An aspect of the invention provides a silicon-based quantum devicecomprising a first metallic structure and a second metallic structurelaterally separated from the first metallic structure. The devicecomprises an elongate channel defined by the separation between thefirst and second metallic structures; the elongate channel has a vertex.The device comprises a third metallic structure which is positionedpartially in the elongate channel. The device further comprises a fourthmetallic structure arranged at a first end of the third metallicstructure and a fifth metallic structure arranged at a second end of thethird metallic structure. The first, second, third, fourth and fifthmetallic structures are configured for connection to first, second,third, fourth and fifth electric potentials respectively, and the first,second, third, fourth and fifth electric potentials are controllable todefine an electrical potential well to confine quantum charge carriersin an elongate quantum dot beneath the elongate channel. The fourth andfifth electric potentials and the position of the fourth and fifthmetallic structures define first and second ends of the elongate channelrespectively. The width of the electrical potential well is defined bythe position of the first, second and third metallic structures andtheir corresponding electric potentials; and the length of theelectrical potential well is defined by the position of the third,fourth and fifth metallic structures and their corresponding electricpotentials. The third electric potential is controllable to adjustquantum charge carrier energy levels in the electrical potential well.

This device provides a quasi-one-dimensional channel with improvedconfinement of quantum charge carriers. The quasi-one-dimensionalchannel extends around a corner. The charge carriers may for example beelectrons or holes. The elongate channel can support an elongatedquantum dot having a vertex which can advantageously be used to couplelaterally separated conductive regions of the device. Beneficially, theelongated quantum dot which extends around a corner can be used tofabricate two dimensional arrays whilst only using planar routing. Thedevice also beneficially provides improved control over the chargecarrier occupation within the electrical potential well.

The presence of first and second metallic structures either side of thethird metallic structure provides improved individual control of theshape of the channel and the chemical potential levels within thepotential well. Advantageously, this device provides the capability fordifferent structures within the device to be brought into resonance.

Advantageously, the fourth and fifth electric potentials may beconfigured such that the fourth and fifth metallic structures form anelectrostatic barrier to define the length of the elongate channeltogether with the third metallic structure. The width of the elongatechannel is typically defined using the first, second and third metallicstructures.

Furthermore, the application of first and second electric potentials tothe first and second metallic structures respectively reduces the effectof the application of the fourth and fifth electric potentials on theshape of the elongate channel. Advantageously, the shape of the elongatechannel is primarily controlled using the first and second electricpotentials.

The device comprises an elongate channel which has a vertex. The thirdmetallic structure is positioned partially in the elongate channel andtherefore typically the third metallic structure extends around thevertex. This has an advantage that the device structure can be scaled upto couple conductive regions arranged in a two dimensional array.Typically the outer edges of the third metallic structure substantiallyalign with the inner edges of the elongate channel.

The first, second, third, fourth and fifth metallic structures areconfigured for connection to respective electric potentials which arecontrollable to define an electrical potential well to confine quantumcharge carriers in an elongate quantum dot beneath the elongate channel.The first, second, third, fourth and fifth metallic structures definethe width and length of the electrical potential well. Therefore theelongate quantum dot typically extends around the vertex. This has anadvantage that an elongate quantum dot having a vertex can be used as amediator dot between conductive regions in a two dimensional array wherea straight elongate quantum dot would not be suitable. The configurationprovides a mediation mechanism compatible with planar routing.

Typically the device further comprises a substrate beneath the first,second and third metallic structures. The substrate may comprise anisotopically purified silicon layer, for example silicon-28. Thesubstrate may further comprise additional silicon layers beneath thesilicon-28 layer. The device is preferably a silicon metal oxidesemiconductor (SiMOS) device.

The first, second, third, fourth and fifth electric potentials arepreferably configured to define the dimensions and charge carrieroccupation of the electrical potential well. Preferably, the polarity ofthe first and second electric potentials is opposite to the polarity ofthe third electric potential.

Typically, the first electric potential is substantially the same as thesecond electric potential. The first and second electric potentialspreferably define first and second walls of the electrical potentialwell. The use of similar or the same electric potentials to define thefirst and second walls results in a substantially symmetrical electricalpotential well which advantageously provides a more uniform confinementregion. This may be achieved by providing electrical contact between thefirst and second metallic structures or providing them in a commonlayer.

Optionally, the fourth electric potential is substantially the same asthe fifth electric potential. This may provide an advantage ofuniformity of quantum charge carrier confinement. In another example,the fourth electric potential and the fifth electric potential may bedifferent. The fourth and fifth electric potentials affect the height ofthe electric potential barrier at the first and second ends of theelongate channel. The fourth and fifth electric potentials may bealtered to change the barrier height and accordingly the tunnellingstrength in and out of the electrical potential well. Advantageouslythis allows an experimentalist to manipulate the quantum charge carriersas desired.

The first and second metallic structures typically extend to an outerregion of the device. In the outer region, the first and second metallicstructures can be connected to a voltage source which is configured tosupply a potential bias. The magnitude and polarity of the bias can beselected according to the desired characteristics of the device andspecifically the electrical potential well.

The first metallic structure and the second metallic structure may beconnected to two separate voltage sources or may be connected to thesame voltage source. Optionally, if the first and second metallicstructures are connected to the same voltage source, the first andsecond metallic structures may form a single structure with first andsecond limbs such that the first and second metallic structures arepositioned either side of the elongate channel. In this case, the use ofa single structure to form both the first metallic structure and thesecond metallic structure ensures the electrical connection between thetwo. Optionally, if the first metallic structure and the second metallicstructure are connected to two separate voltage sources, the set voltagemay nevertheless be selected to be the same on each of the voltagesources.

Advantageously, if the first and second electric potentials aresubstantially the same, the walls of the electrical potential well willbe substantially symmetrical and will thus provide good confinement.

Optionally, the first and second metallic structures are arranged in afirst metallic layer. A plurality of metallic structures may bedeposited simultaneously so as to form a single layer in which eachstructure, separated laterally, is approximately the same thickness.This advantageously reduces the number of steps required to manufacturethe device. The third metallic structure may be arranged in a secondmetallic layer.

Preferably, the device further comprises an electrically insulatinglayer between the first metallic layer and the second metallic layer andoverlying the first metallic layer. This beneficially provides anelectrical separation between the metallic layers which allows thefirst, second and third metallic structures to be connected to differentelectric potentials.

Optionally, the fourth and fifth metallic structures may be arranged ina third metallic layer. Preferably, the device further comprises anotherelectrically insulating layer between the second metallic layer and thethird metallic layer. Advantageously the presence of electricallyinsulating layers in between metallic layers separates the conductingregions which adds flexibility to the device structure.

Typically, each of the first metallic layer and the second metalliclayer comprises a plurality of laterally separated metallic structures.Optionally, the third metallic layer comprises a plurality of laterallyseparated metallic structures. The use of multiple metallic structuresin one or more of the metallic layers provides additional flexibility tothe device structure.

The second metallic layer may further comprise a sixth metallicstructure configured for connection to a sixth electric potential.Preferably, a reservoir of charge carriers can be supported beneath thesixth metallic structure. The reservoir may be couplable to theelectrical potential well by proximity. The strength of coupling may bedetermined by a modifiable electric potential barrier, the height ofwhich may be modified by one or more of the plurality of metallicstructures in the third metallic layer for example. Advantageously, thecoupling of the reservoir to the potential well improves chargestability of the potential well.

The second metallic layer may further comprise a seventh metallicstructure configured for connection to a seventh electric potential.Preferably, a quantum dot can be supported beneath the seventh metallicstructure. The quantum dot may be couplable to the electrical potentialwell by proximity. The strength of coupling may be determined by amodifiable electric potential barrier, the height of which may bemodified by one or more of the plurality of metallic structures in thethird metallic layer for example. Additional quantum dots may besupported beneath additional metallic structures in the second metalliclayer. For example, a first quantum dot may be supported near the firstend of the electrical potential well and a second quantum dot may besupported near the second end of the electrical potential well.Advantageously, the electrical potential well may be used to communicatequantum information between the first and second quantum dots.

The device may comprise additional metallic structures which can each beconfigured to induce a quantum dot. The device may therefore be suitablefor supporting an array of quantum dots which may be used as qubits inquantum computations. Each quantum dot in the array of quantum dots maybe coupled to another quantum dot, an electrical potential well, or acharge carrier reservoir. The device advantageously provides a mechanismfor coupling quantum dots and for individually addressing large numbersof quantum dots in a single device.

Preferably, the device further comprises one or more implanted regions.For example, a metallic structure in the second metallic layer maypartially overly one of the one or more implanted regions. Thisadvantageously results in ohmic contact between the metallic structureand the substrate. The implanted region typically comprises a group Vion such as phosphorus (P⁺). The metallic structure may for example beconfigured to support a quantum charge carrier reservoir or a quantumdot.

The first and second metallic structures are laterally separated,defining the elongate channel in between. The third metallic structureis positioned partially in the elongate channel. The elongate channel ispreferably longer than it is wide and has a vertex. Preferably, a firstportion of the channel is angled with respect to a second portion of thechannel. In this way the channel, and the consequent elongate quantumdot formed beneath the third metallic structure, extends around acorner. Advantageously, this configuration provides a mechanism forfabricating two dimensional arrays whilst only using planar routing.

Each of the metallic structures is typically configured for connectionto a respective electric potential, defining an electric potentialtopography across the device. Typically, each of the metallic structuresextends to an outer region of the device where they can be connected toa voltage source which can be used to supply a particular potentialbias. In particular, the third metallic structure may comprise a firstextension, wherein the first extension partially overlies the firstmetallic structure. The first extension may be configured for connectionto the third electric potential and typically connects the portion ofthe third metallic structure positioned within the elongate channel andthe voltage source.

The third metallic structure may further comprise a second extensionwhich partially overlies the first metallic structure. The first and/orsecond extension may be configured for connection to the third electricpotential. The use of two extensions advantageously provides a mechanismfor troubleshooting the device, by using the first extension to connectthe third metallic structure to the third electric potential and usingthe second extension to check the correct function of the firstextension.

Another aspect of the invention provides a method of manufacturing asilicon-based quantum device. The method comprises: depositing a firstmetallic structure; depositing a second metallic structure laterallyseparated from the first metallic structure such that an elongatechannel is defined by the separation between the first and secondmetallic structures; wherein the elongate channel has a vertex;depositing a third metallic structure partially in the elongate channel;depositing a fourth metallic structure at a first end of the thirdmetallic structure; depositing a fifth metallic structure at a secondend of the third metallic structure; wherein the first, second, third,fourth and fifth metallic structures are configured for connection tofirst, second, third, fourth and fifth electric potentials respectively;wherein the first, second, third, fourth and fifth electric potentialsare controllable to define an electrical potential well to confinequantum charge carriers in an elongate quantum dot beneath the elongatechannel. The fourth and fifth electric potentials and the position ofthe fourth and fifth metallic structures define first and second ends ofthe elongate channel respectively. The width of the electrical potentialwell is defined by the position of the first, second and third metallicstructures and their corresponding electric potentials; and the lengthof the electrical potential well is defined by the position of thethird, fourth and fifth metallic structures and their correspondingelectric potentials. The third electric potential is controllable toadjust quantum charge carrier energy levels in the electrical potentialwell.

Advantageously, this method of manufacturing a silicon-based deviceprovides a confinement region in which quantum charge carriers can beconfined. The elongate channel can support an elongated quantum dotwhich can advantageously be used to couple laterally separatedconductive regions of the device such as charge carrier reservoirs orquantum dots.

Typically, depositing the third metallic structure partially in theelongate channel comprises depositing the third metallic structureextending around the vertex. The third metallic structure is preferablypartially deposited in the elongate channel and partially depositedoverlying the first metallic structure. Typically the first, second,fourth and fifth metallic structures define the extent of the elongatechannel. The portion of the third metallic structure deposited in theelongate channel typically substantially fills the elongate channel. Forexample, edges of the third metallic structure may overly or abut theedges of one or more of the first, second, fourth and fifth metallicstructures. An advantage of depositing the third metallic structureextending around the vertex is the ability to manufacture a device thatcan support a two dimensional array of quantum dots using planarrouting.

As a consequence of a third metallic structure being deposited extendingaround the vertex, the elongate quantum dot typically extends around thevertex. An advantage of this is the ability to mediate interactionsaround a corner in a quantum device.

Preferably, the first and second metallic structures are depositedsimultaneously as part of a first metallic layer. The deposition of thefirst and second metallic structures in the same fabrication stepadvantageously reduces the number of fabrication steps required tomanufacture the device and therefore reduces the manufacturingcomplexity. The third metallic structure may be deposited as part of asecond metallic layer following the deposition of the first metalliclayer.

The first and second metallic structures are preferably deposited on asilicon substrate to create a silicon metal oxide semiconductor (SiMOS)device.

The method typically further comprises depositing a first electricallyinsulating layer after depositing the first metallic layer and beforedepositing the second metallic layer. The first electrically insulatinglayer preferably overlies the first metallic layer. This advantageouslyelectrically separates the first and second metallic structures from thethird metallic structures, allowing the first and second electricpotentials to differ from the third electric potential.

After the deposition of the second metallic layer, the fourth and fifthmetallic structures are preferably deposited simultaneously as part of athird metallic layer. The method typically further comprises depositinga second electrically insulating layer after depositing the secondmetallic layer and before depositing the third metallic layer, whereinthe second electrically insulating layer overlies the second metalliclayer.

The method preferably further comprises creating one or more implantedregions in the silicon substrate before metal deposition. For example,phosphorus ions may be implanted to create negatively doped regions inthe device. A metallic structure in the second metallic layer may bepositioned such that a portion of the metallic structure extends tocover or partially cover one of the one or more implanted regions.Advantageously this results in ohmic contact between the metallicstructure and the substrate.

A further aspect of the invention provides a method of operating asilicon-based quantum device. The method comprises: applying a firstelectric potential to a first metallic structure; applying a secondelectrical potential to a second metallic structure, wherein the secondmetallic structure is laterally separated from the first metallicstructure such that an elongate channel is defined by the separationbetween the first and second metallic structures; wherein the elongatechannel has a vertex; applying a third electric potential to a thirdmetallic structure, wherein the third metallic structure is positionedpartially in the elongate channel; applying a fourth electric potentialto a fourth metallic structure arranged at a first end of the thirdmetallic structure; applying a fifth electric potential to a fifthmetallic structure arranged at a second end of the third metallicstructure; and controlling the third electric potential to adjustquantum charge carrier energy levels in the electrical potential well.The first, second, third, fourth and fifth metallic structures areconfigured for connection to first, second, third, fourth and fifthelectric potentials respectively. The first, second, third, fourth andfifth electric potentials are controllable to define an electricalpotential well to confine quantum charge carriers in an elongate quantumdot beneath the elongate channel; and the fourth and fifth electricpotentials and the position of the fourth and fifth metallic structuresdefine first and second ends of the elongate channel respectively. Thewidth of the electrical potential well is defined by the position of thefirst, second and third metallic structures and their correspondingelectric potentials; and the length of the electrical potential well isdefined by the position of the third, fourth and fifth metallicstructures and their corresponding electric potentials.

Advantageously, this method can be used to operate a two dimensionalarray of quantum dots whilst only using planar routing.

Typically, the third metallic structure extends around the vertex. Thethird electric potential is applied to the third metallic structure andthe third electric potential can be controlled to adjust quantum chargecarrier energy levels in the electrical potential well. Advantageously,when the third metallic structure has a vertex, the third electricpotential can be controlled to define an electrical potential wellhaving a vertex. This can be used to operate a device which supports atwo dimensional array of quantum dots.

Consequently, the elongate quantum dot typically extends around thevertex. Advantageously, an elongate quantum dot extending around avertex can be used to mediate interactions around a corner.

Preferably the polarity of the first and second electric potentials isopposite to the polarity of the third electric potential. Advantageouslythis enhances the confinement of quantum charge carriers in the elongatequantum dot. The first and second metallic structures and thecorresponding electric potentials typically provide electrostaticbarriers on each side of the third metallic structure. The thirdmetallic structure and the third electric potential preferably provide aplunger gate.

Typically, the first electric potential is substantially the same as thesecond electric potential. The first and second electric potentialspreferably define first and second walls of the electrical potentialwell. The use of similar or the same electric potentials to define thefirst and second walls results in a substantially symmetrical electricalpotential well which advantageously provides a more uniform confinementregion. This may be achieved by providing electrical contact between thefirst and second metallic structures or providing them in a commonlayer.

Optionally, the fourth electric potential is substantially the same asthe fifth electric potential. This may provide an advantage ofuniformity of quantum charge carrier confinement. In another example,the fourth electric potential and the fifth electric potential may bedifferent. The fourth and fifth electric potentials affect the height ofthe electric potential barrier at the first and second ends of theelongate channel. The fourth and fifth electric potentials may bealtered to change the barrier height and accordingly the tunnellingstrength in and out of the electrical potential well. Advantageouslythis allows an experimentalist to manipulate the quantum charge carriersas desired.

Another aspect of the invention provides a silicon-based quantum devicecomprising a first metallic structure, a second metallic structure and athird metallic structure. The first metallic structure is configured forconnection to a first electric potential. The second metallic structureis configured for connection to a second electric potential. The thirdmetallic structure, positioned at least partially in an elongate channelbetween the first and second metallic structures, is configured forconnection to a third electric potential so that an electrical potentialwell is defined by the electric potentials of the first, second andthird metallic structures to confine quantum charge carriers beneath theelongate channel. The third electric potential is controllable to adjustquantum charge carrier energy levels in the electrical potential well.

A further aspect of the invention provides a method of manufacturing asilicon-based quantum device. The method comprises: depositing first andsecond metallic structures; and depositing a third metallic structure atleast partially in an elongate channel between the first and secondmetallic structures; wherein the first, second and third metallicstructures are configured for connection to first, second and thirdelectric potentials respectively so that an electrical potential well isdefined by the first, second and third electric potentials to confinequantum charge carriers beneath the elongate channel. The third electricpotential is controllable to adjust quantum charge carrier energy levelsin the electrical potential well.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings in which:

FIG. 1A is a cross-sectional side view of a silicon-based quantum devicein accordance with a first embodiment of the invention;

FIG. 1B is a top view of a silicon-based quantum device in accordancewith the first embodiment of the invention;

FIG. 2 is a top view of a silicon-based quantum device;

FIG. 3 is a top view of a silicon-based quantum device;

FIG. 4 is a top view of a silicon-based quantum device;

FIG. 5 is a top view of a silicon-based quantum device;

FIG. 6A is a cross-sectional side view of an elongate channel; and

FIG. 6B is a schematic of a potential energy landscape.

DETAILED DESCRIPTION

FIGS. 1A and 1B schematically illustrate a cross-sectional side view anda top view of a silicon-based quantum device according to a firstembodiment. The silicon-based quantum device is made using siliconmetal-oxide semiconductor, or SiMOS, fabrication processes. Thecross-sectional side view depicted in FIG. 1A is along the direction Aindicated in FIG. 1B.

FIG. 1A shows a first metallic structure 101, a second metallicstructure 102 and a third metallic structure 103 on a silicon substrate100. In this embodiment, the first and second metallic structures 101,102 are deposited simultaneously, i.e. in the same processing step, andare therefore approximately the same thickness. The first and secondmetallic structures 101, 102 are arranged in a first metallic layer 111.The first and second metallic structures 101, 102 are laterallyseparated within the first metallic layer 111, forming an elongatechannel 120 between them.

The third metallic structure 103 is deposited partially in the elongatechannel 120 between the first metallic structure 101 and the secondmetallic structure 102. The third metallic structure 103 is arranged ina second metallic layer 112. An electrically insulating layer (notshown) is deposited between the first metallic layer 111 and the secondmetallic layer 112. The electrically insulating layer may be formed fromany suitable material such as alumina or any high-k dielectric.

Each of the first, second and third metallic structures 101, 102 and 103are deposited on the silicon substrate 100, the top layer of which isisotopically purified silicon, silicon-28 in this embodiment. The first,second and third metallic structures 101, 102 and 103 may be formed fromany suitable metal such as gold or tungsten. Each of the first andsecond metallic layers 111, 112 may comprise multiple layers. Forexample one of the first or second metallic layers 111, 112 may comprisea layer of titanium followed by a layer of gold. The deposition of metalmay be performed using any suitable technique such as atomic layerdeposition or chemical vapour deposition.

FIG. 1B schematically illustrates a top view of the silicon-basedquantum device shown in FIG. 1A. The first metallic layer 111 includes aplurality of metallic structures including the first metallic structure101 and the second metallic structure 102. The first and second metallicstructures 101, 102 in the first metallic layer 111 are configured forconnection to first and second electric potentials respectively. Thefirst and second electric potentials may be substantially the same, andmay be tuned to form confinement regions in the device by forming anelectrostatic potential barrier.

The second metallic layer 112 includes a plurality of metallicstructures including the third metallic structure 103. A first portion121 of the third metallic structure 103 is positioned in the elongatechannel 120 between the first and second metallic structures 101, 102and a second portion 122 of the third metallic structure 103 ispositioned partially overlying the first metallic structure 101. Thewidth of the first metallic structure 101, which defines the level ofoverlap between the second portion 122 of the third metallic structure103 and the first metallic structure 101, can be adjusted according tofabrication considerations. The first metallic structure 101 should bewide enough to provide adequate confinement and narrow enough to reducethe likelihood of a defect in the electrically insulating layer betweenthe first and third metallic structures 101, 103. For example, the firstmetallic structure 101 may be between 10 and 400 nanometres when usingplanar routing, or between 10 and 50 nanometres when using non-planarrouting. The second portion 122 of the third metallic structure 103 is afirst extension which extends to an outer region of the device and isconfigured for connection to a third electric potential. The thirdmetallic structure 103 in this embodiment is ‘T’ shaped, when viewedfrom above.

The third metallic structure 103 acts as a plunger gate, and the first,second and third electric potentials are tuned such that an electricalpotential well is defined beneath the elongate channel 120. Theelectrical potential well beneath the elongate channel 120 is anelongated quantum dot, or a mediator quantum dot. The presence of thefirst and second metallic structures 101, 102 on either side of thethird metallic structure 103 provides improved control of theconfinement shape of the elongated quantum dot beneath the elongatechannel 120.

Quantum charge carriers such as electrons or holes can be confined inthe elongated quantum dot. The third electric potential has the oppositepolarity to the first and second electric potentials and can be adjustedto control the number of charge carriers in the elongated quantum dot.For example, if the first and second electric potentials are negative,the third electric potential is positive. Altering the third electricpotential has the effect of shifting the depth of the electricalpotential well and correspondingly shifting the quantum charge carrierenergy levels within the potential well. This can be used to modify thenumber of quantum charge carriers confined within the elongated quantumdot.

A fourth metallic structure 104 and a fifth metallic structure 105 formbarrier gates. In this embodiment, the fourth and fifth metallicstructures 104, 105 are deposited simultaneously and form part of athird metallic layer 113. The third metallic layer 113 comprises aplurality of metallic structures. The fourth and fifth metallicstructures 104, 105 are configured for connection to fourth and fifthelectric potentials respectively. The fourth and fifth electricpotentials are chosen such that the fourth and fifth metallic structures104, 105 define a first end 114 and a second end 115 of the elongatechannel 120 respectively by forming potential barriers. The fourth andfifth electric potentials can be controlled to adjust the height of thepotential barriers at the respective ends of the elongate channel 120.

The electrical potential well, positioned beneath the elongate channel120, is accordingly defined by the first, second, third, fourth andfifth metallic structures 101-105 and their corresponding electricpotentials. The width of the electrical potential well is defined by thefirst, second and third metallic structures 101-103 and electricpotentials; the length of the electrical potential well is defined bythe third, fourth and fifth metallic structures 103-105 and electricpotentials.

In this embodiment, the fabrication of the device includes depositingthe first metallic layer 111, depositing a first electrically insulatinglayer (not shown) over the first metallic layer 111, depositing thesecond metallic layer 112, depositing a second electrically insulatinglayer (not shown) over the second metallic layer 112, and depositing thethird metallic layer 113. In this way, the first, second and thirdmetallic layers 111, 112, 113 are electrically separated. In analternative embodiment, the third metallic layer is deposited before thesecond metallic layer, with an electrically insulating layer positionedbetween each metallic layer. Each electrically insulating layer isconfigured to cover a previously deposited, and thus exposed, metalliclayer. Each electrically insulating layer may partially cover theexposed metallic layer. Importantly, each electrically insulating layeris deposited such that each metallic layer is electrically separatedfrom each of the other metallic layers. There is no galvanic contactbetween the metallic layers and therefore charge carriers do not flowbetween vertically stacked metallic layers.

In this embodiment, the second metallic layer 112 further comprisesthree additional metallic structures acting as plunger gates. A firstplunger gate 131 is suitable for supporting a reservoir of chargecarriers. A second plunger gate 132 forms a source of quantum chargecarriers and a third plunger gate 133 forms a drain for quantum chargecarriers. In an alternative embodiment, the second plunger gate may forma drain for quantum charge carriers and the third plunger gate may forma source of quantum charge carriers.

Each of the first, second and third plunger gates 131, 132, 133 aredeposited at the same time as the third metallic structure in thisembodiment, and are each configured for connection to respectiveelectric potentials. The electric potentials may be adjusted accordingto the required device function. For example, there may be a potentialdifference between the electric potential on the second plunger gate andthe electric potential on the third plunger gate such that the movementof charge carriers is in a particular direction. Each of the first,second and third plunger gates 131, 132, 133 are positioned to partiallyoverly an implanted region (not shown) of the device. The implantedregion comprises ions such as phosphorus ions and is typicallypositioned in an outer region of the device.

The fourth metallic structure 104 in the third metallic layer 113 ispositioned between the first end 114 of the third metallic structure 103and the second plunger gate 132 of the second metallic layer 112. Thefifth metallic structure 105 in the third metallic layer 113 ispositioned between the second end 115 of the third metallic structure103 and the third plunger gate 133 of the second metallic layer 112. Thefourth and fifth metallic structures 104, 105 are partially positionedin a channel between two metallic structures of the first metallic layer111, and partially positioned overlying the first metallic structure101. Adjusting the fourth and fifth electric potentials adjusts theheight of the potential barriers formed beneath the fourth and fifthmetallic structures which controls the tunnel coupling between adjacentelectrical potential wells. In this embodiment, adjusting the electricpotential on the barrier gates 104, 105 controls the strength of thecoupling between the metallic structures in the third metallic layer,namely the second plunger gate 132, the third metallic structure 103 andthe third plunger gate 133.

The third metallic layer 113 comprises barrier gates including thefourth metallic structure 104 and the fifth metallic structure 105. Thethird metallic layer 113 further comprises an additional barrier gate, afirst barrier gate 130, which is positioned between the first plungergate 131 and the third metallic structure 103. The first barrier gate130 is configured for connection to a barrier potential which can beadjusted to control the coupling strength between the reservoir ofcharge carriers, supported beneath the first plunger gate 131, and theelongated quantum dot supported beneath the third metallic structure103.

The first metallic layer comprises an additional metallic structure: afirst confinement gate, 123. A first channel 124 is formed between thefirst metallic structure 101 and the first confinement gate 123 and thesecond metallic structure 102. The second plunger gate 132, the fourthmetallic structure 104, the third metallic structure 103, the fifthmetallic structure 105 and the third plunger gate 133 are all partiallypositioned within the first channel 124. The elongate channel 120beneath which quantum charge carriers can be confined forms a portion ofthe first channel 124. A second channel 125 is formed between the secondmetallic structure 102 and the first confinement gate 123. The firstbarrier gate 130 and the first plunger gate 131 are positioned partiallywithin the second channel 125.

Each of the metallic structures is configured for connection to arespective electric potential. In this way, an electric potentialtopography is built up on the surface of the device, across whichquantum charge carriers can be manipulated and guided. Each of themetallic structures extends out to an outer region of the device to abonding region, which can be used to connect the metallic structure to avoltage source. The metallic structures in the first metallic layerremain substantially adjacent to the metallic structures in the secondmetallic layer even in the outer region of the device to minimise thepresence of unwanted charge carriers. However, a small separation may beintroduced between the metallic structures of the first and secondmetallic layers in order to avoid defects in the underlying substrate.The metallic structures in the first metallic layer can be used toscreen electric potentials arising from the metallic structures in thesecond and/or third metallic layers.

Quantum charge carriers are confined within electrical potential wellsbeneath the third metallic structure 103, and the first, second andthird plunger gates 131, 132, 133. The fourth and fifth metallicstructures 104, 105 and the first barrier gate 130 form potentialbarriers, and the first and second metallic structures 101, 102 and thefirst confinement gate 123 form potential walls. The electric potentialsare adjustable during operation in order to move charge carriers withinthe device. In particular, the electric potentials of the metallicstructures 104, 105, 130 in the third metallic layer 113 can be adjustedto control the strength of coupling between neighbouring charge carrierconfinement regions, and the electric potentials of the metallicstructures 103, 131, 132, 133 in the second metallic layer 112 can becontrolled to adjust the quantum charge carrier energy levels in theelectrical potential wells or confinement regions, thus adjusting thequantum charge carrier occupancy.

FIG. 2 schematically illustrates a top view of a silicon-based quantumdevice. A first metallic layer 311 comprises a plurality of confinementgates which define a first channel 324 and a second channel 325. Asecond metallic layer 312 comprises a plurality of plunger gatesincluding a source gate 314, a drain gate 316, a mediator gate 318 and areservoir gate 319. A third metallic layer 313 comprises a plurality ofbarrier gates.

The first channel 324 includes a portion of the source gate 314, thedrain gate 316, the mediator gate 318, four quantum dot gates 305, 306,307, 308 and six barrier gates 331, 332, 333, 334, 335, 336. Eachplunger gate 305-308, 314, 316, 318 is separated by a barrier gate331-336. The electric potential of the barrier gates 331-336 can beadjusted to control the strength of the coupling between adjacentplunger gates. The electric potentials of the plunger gates, in use, areconfigured such that an electrical potential well is defined beneath theplunger gates within the first channel.

The second channel 325 includes a portion of the reservoir gate 319surrounded by a seventh barrier gate 337. The electric potential of theseventh barrier gate 337 can be tuned to adjust the strength of thecoupling between the reservoir and the elongated quantum dot supportedbeneath the mediator gate 318.

The source gate 314, the drain gate 316 and the reservoir gate 319extend to a doped region to provide ohmic contact.

The portion of the device shown in FIG. 2 illustrates four quantum dots301, 302, 303, 304. Neighbouring quantum dots, i.e. the first and secondquantum dots 301, 302 and the third and fourth quantum dots 303, 304,can interact. The second and third quantum dots 302, 303 can alsointeract using the elongated quantum dot 300 which acts as a mediator.

FIG. 3 schematically illustrates a top view of a silicon-based quantumdevice. The device is similar to the device shown in FIG. 1B. A firstmetallic layer 411 has metallic structures which form confinement gatesdefining channels. A second metallic layer 412 has metallic structureswhich form plunger gates including a source gate 414, a drain gate 416,a mediator gate 418 and a reservoir gate 419. A third metallic layer 413has metallic structures which form barrier gates separating the mediatorgate 418 from the source and drain gates 414, 416 and separating themediator gate from the reservoir gate 419. The electric potentialapplied to the metallic structures in the third metallic layer 413 canbe controlled to control the coupling strength between neighbouringquantum charge carrier confinement regions. The confinement regions aretypically in the form of electrical potential wells such as theelectrical potential well formed beneath an elongate channel 420 inwhich the mediator gate 418 is partially positioned.

This embodiment differs from that shown in FIG. 1B in that the thirdmetallic structure 403 comprises an additional extension. The thirdmetallic structure 403 which forms the mediator gate 418 comprises afirst portion 421, a second portion 422 and a third portion 423. Thefirst portion 421 is positioned in the elongate channel 420 betweenlaterally separated metallic structures 401 within the first metalliclayer 411. The second portion 422 and the third portion 423 of the thirdmetallic structure 403 extend substantially parallel to each other andsubstantially perpendicular to the first portion 421 to an outer regionof the device. The second and third portions 422, 423 are first andsecond extensions of the mediator gate 418 respectively, extending to anouter region of the device for connection to a voltage source. Either orboth of the second and third portions 422, 423 may be connected to thevoltage source. The third metallic structure, i.e. the mediator gate418, in this embodiment is ‘U’ shaped.

FIG. 4 schematically illustrates a top view of a silicon-based quantumdevice. A first metallic layer 511 comprises a first metallic structure501 and a second metallic structure 502. The first and second metallicstructures 501, 502 are laterally separated so as to define an elongatechannel 520 between them. In this embodiment, the elongate channel 520has a vertex 505.

A second metallic layer 512 comprises a source gate 514, a drain gate516 and a mediator gate 518. The source gate 514 is an elongate metallicstructure and is positioned at an angle to the drain gate 516 of similarstructure. The mediator gate 518 is positioned in the elongate channel520 and extends around the vertex 505. A first region of the mediatorgate 518 is angled with respect to a second region of the mediator gate518 and the first and second regions are positioned within the elongatechannel 520. The first region of the mediator gate 518 is axiallyaligned with the source gate 514 (horizontally from the perspective ofFIG. 4 ) and the second region of the mediator gate 518 is axiallyaligned with the drain gate 516 (vertically from the perspective of FIG.4 ). In this embodiment, the angle between the source and drain gates514, 516 and first and second regions of the mediator gate 518 isapproximately a right angle. For example, the angle may be between 85and 95 degrees and is preferably between 89 and 91 degrees. Inalternative embodiments, the angle may be approximately 45 degrees or135 degrees. The mediator gate 518 has a first portion 521 which ispositioned within the elongate channel 520 and a second portion 522which extends from the mediator gate 518 to an outer region of thedevice.

A third metallic layer 513 comprises a first barrier gate 531 and asecond barrier gate 532. The first barrier gate is positioned betweenthe source gate 514 and the mediator gate 518. The second barrier gateis positioned between the mediator gate 518 and the drain gate 516.

Using this device structure, it is possible to mediate interactionsaround a corner. This allows two-dimensional arrays of quantum dots tobe addressed within a device using planar routing. In anotherembodiment, the device may include a quantum dot gate and an additionalbarrier gate between the mediator gate and the source and/or drain gate.The elongate quantum dot can be formed with a vertex beneath themediator gate.

FIG. 5 schematically illustrates a top view of a silicon-based quantumdevice. A first metallic layer 711 comprises a plurality of metallicstructures which together define a first channel 724 and a secondchannel 725. A second metallic layer 712 comprises first and secondquantum dot gates 705, 706, first and second source gates 714, 715, andfirst and second drain gates 716, 717. A third metallic layer 713comprises first and second barrier gates 731, 732. The barrier gates731, 732 are positioned substantially perpendicular to the first andsecond channels 724, 725 and each barrier gate is partially positionedin each channel.

Accordingly, the first channel 724 includes portions of the first sourcegate 714, the first quantum dot gate 705 and the first drain gate 716separated by the first and second barrier gates 731, 732. The secondchannel 725 includes portions of the second source gate 715, the secondquantum dot gate 706 and the second drain gate 716 which are alsoseparated by the first and second barrier gates 731, 732.

In this embodiment, one of the plurality of metallic structures in thefirst metallic layer 711 forms a horizontal confinement gate 720. Thehorizontal confinement gate 720 provides a barrier between the firstchannel 724 and the second channel 725 such that the first and secondchannels 724, 725 can support linear arrays of quantum dots and/ormediator dots. This device structure therefore provides a mechanism foraddressing neighbouring linear arrays of quantum dots using only planarrouting.

FIG. 6B schematically illustrates the electric potential landscape 800along the elongate channel 820 illustrated in FIG. 6A. FIG. 6A is across-sectional view of the elongate channel 820 and depicts a sourceelectrode 814, a mediator electrode 818 and a drain electrode 816separated by a first barrier electrode 831 and a second barrierelectrode 832. The source, drain and mediator electrodes 814, 816, 818are metallic structures within the second metallic layer 812. The firstand second barrier electrodes 831, 832 are metallic structures withinthe third metallic layer 813. The first metallic layer is positionedeach side of the elongate channel and is therefore not shown in thecross-sectional view.

Each of the metallic structures 814, 831, 818, 832, 816 within theelongate channel 820 are configured for connection to correspondingelectric potentials. These electric potentials define a potential energylandscape 800 along the elongate channel 820. Lateral confinement of thequantum charge carriers within the elongate channel 820 is achievedusing the electric potentials of the confinement electrodes in the firstmetallic layer. FIG. 6B depicts an exemplary potential energy landscape800. However, the electric potentials of each of the metallic structures814, 831, 818, 832, 816 within the elongate channel 820 can be adjustedto modify the potential energy landscape 800 according to requirements.

The potential energy landscape 800 includes first, second and thirdpotential wells 841, 842, 843. The first potential well 841 is formedbeneath the mediator electrode 818. The second and third potential wells842, 843 are formed beneath the source and drain electrodes 814, 816respectively. In this embodiment, the electric potential of the sourceand drain electrodes 814, 816 is substantially the same and is less thanthe electric potential of the mediator electrode 818. Accordingly, thefirst potential well 841 is deeper than the second and third potentialwells 842, 843 and the second and third potential wells 842, 843 are asimilar depth.

The number of quantum charge carriers confined within a potential wellis related to the depth of the potential well. FIG. 6B illustrates thetop-most energy levels 851, 852, 853 within each of the first, secondand third potential wells 841, 842, 843 respectively. Quantum chargecarriers are illustrated occupying the top-most energy levels 851-853 inone possible configuration.

The potential energy landscape 800 also includes first and secondbarriers 844, 845 formed beneath the first and second barrier electrodes831, 832 respectively. The first barrier 844 separates the secondpotential well 842 from the first potential well 841. The second barrier845 separates the third potential well 843 from the first potential well841. The electric potentials of the first and second barrier electrodes831, 832 can be adjusted to control the tunnel coupling between adjacentpotential wells. Control of the tunnel coupling can be used to adjustthe quantum charge carrier occupation within each potential well841-843.

As will be appreciated, a silicon-based quantum device is disclosedalong with a method of manufacturing the device. Each of thesilicon-based quantum devices as described include a series of metalliclayers which are deposited sequentially. Electrically insulating layersare deposited in between each of the metallic layers in order toelectrically separate the metallic layers. Each of the metallic layerscomprise a plurality of metallic structures. Each of the metallicstructures are configured for connection to respective electricpotentials. The relative arrangement of the metallic structures and theelectric potentials together define an electrical potential topographywhich can be used to manipulate quantum charge carriers such aselectrons or holes within the device.

1. A silicon-based quantum device comprising: a first metallicstructure; a second metallic structure laterally separated from thefirst metallic structure; an elongate channel defined by the separationbetween the first and second metallic structures; wherein the elongatechannel has a vertex; a third metallic structure positioned partially inthe elongate channel; a fourth metallic structure arranged at a firstend of the third metallic structure; a fifth metallic structure arrangedat a second end of the third metallic structure; wherein the first,second, third, fourth and fifth metallic structures are configured forconnection to first, second, third, fourth and fifth electricpotentials, respectively; wherein the first, second, third, fourth andfifth electric potentials are controllable to define an electricalpotential well to confine quantum charge carriers in an elongate quantumdot beneath the elongate channel; wherein the fourth and fifth electricpotentials and the position of the fourth and fifth metallic structuresdefine first and second ends of the elongate channel, respectively;wherein the width of the electrical potential well is defined by theposition of the first, second and third metallic structures and theircorresponding electric potentials; and wherein the length of theelectrical potential well is defined by the position of the third,fourth and fifth metallic structures and their corresponding electricpotentials; and wherein the third electric potential is controllable toadjust quantum charge carrier energy levels in the electrical potentialwell.
 2. The device according to claim 1, wherein the third metallicstructure extends around the vertex.
 3. The device according to claim 1,wherein the elongate quantum dot extends around the vertex.
 4. Thedevice according to claim 1, wherein the first and second metallicstructures are arranged in a first metallic layer, wherein the thirdmetallic structure is arranged in a second metallic layer, and whereinthe device further comprises an electrically insulating layer betweenthe first metallic layer and the second metallic layer and overlying thefirst metallic layer.
 5. The device according to claim 4, wherein eachof the first metallic layer and the second metallic layer comprises aplurality of laterally separated metallic structures.
 6. The deviceaccording to claim 5, wherein the second metallic layer furthercomprises a sixth metallic structure configured for connection to asixth electric potential such that a reservoir of charge carriers can besupported beneath the sixth metallic structure.
 7. The device accordingto claim 5, wherein the second metallic layer further comprises aseventh metallic structure configured for connection to a seventhelectric potential such that a quantum dot can be supported beneath theseventh metallic structure.
 8. The device according to claim 1, whereinthe third metallic structure comprises a first extension, wherein thefirst extension partially overlies the first metallic structure, andwherein the first extension is configured for connection to the thirdelectric potential.
 9. The device according to claim 8, wherein thethird metallic structure further comprises a second extension, whereinthe second extension partially overlies the first metallic structure,and wherein the first and/or second extension is configured forconnection to the third electric potential.
 10. A method ofmanufacturing a silicon-based quantum device, wherein the methodcomprises: depositing a first metallic structure; depositing a secondmetallic structure laterally separated from the first metallic structuresuch that an elongate channel is defined by the separation between thefirst and second metallic structures; wherein the elongate channel has avertex; depositing a third metallic structure partially in the elongatechannel; depositing a fourth metallic structure at a first end of thethird metallic structure; depositing a fifth metallic structure at asecond end of the third metallic structure; wherein the first, second,third, fourth and fifth metallic structures are configured forconnection to first, second, third, fourth and fifth electricpotentials, respectively; wherein the first, second, third, fourth andfifth electric potentials are controllable to define an electricalpotential well to confine quantum charge carriers in an elongate quantumdot beneath the elongate channel; wherein the fourth and fifth electricpotentials and the position of the fourth and fifth metallic structuresdefine first and second ends of the elongate channel, respectively;wherein the width of the electrical potential well is defined by theposition of the first, second and third metallic structures and theircorresponding electric potentials; and wherein the length of theelectrical potential well is defined by the position of the third,fourth and fifth metallic structures and their corresponding electricpotentials; and wherein the third electric potential is controllable toadjust quantum charge carrier energy levels in the electrical potentialwell.
 11. The method according to claim 10, wherein depositing the thirdmetallic structure partially in the elongate channel comprisesdepositing the third metallic structure extending around the vertex. 12.The method according to claim 10, wherein the elongate quantum dotextends around the vertex.
 13. The method according to claim 10, whereinthe first and second metallic structures are deposited simultaneously aspart of a first metallic layer, and wherein the third metallic structureis deposited as part of a second metallic layer following the depositionof the first metallic layer, and wherein the method further comprisesdepositing a first electrically insulating layer after depositing thefirst metallic layer and before depositing the second metallic layer,wherein the first electrically insulating layer overlies the firstmetallic layer.
 14. The method according to claim 13, wherein the fourthand fifth metallic structures are deposited simultaneously as part of athird metallic layer, and wherein the method further comprisesdepositing a second electrically insulating layer after depositing thesecond metallic layer and before depositing the third metallic layer,wherein the second electrically insulating layer overlies the secondmetallic layer.
 15. A method of operating a silicon-based quantumdevice, wherein the method comprises: applying a first electricpotential to a first metallic structure; applying a second electricalpotential to a second metallic structure, wherein the second metallicstructure is laterally separated from the first metallic structure suchthat an elongate channel is defined by the separation between the firstand second metallic structures; wherein the elongate channel has avertex; applying a third electric potential to a third metallicstructure, wherein the third metallic structure is positioned partiallyin the elongate channel; applying a fourth electric potential to afourth metallic structure arranged at a first end of the third metallicstructure; applying a fifth electric potential to a fifth metallicstructure arranged at a second end of the third metallic structure;wherein the first, second, third, fourth and fifth metallic structuresare configured for connection to first, second, third, fourth and fifthelectric potentials, respectively; wherein the first, second, third,fourth and fifth electric potentials are controllable to define anelectrical potential well to confine quantum charge carriers in anelongate quantum dot beneath the elongate channel; wherein the fourthand fifth electric potentials and the position of the fourth and fifthmetallic structures define first and second ends of the elongatechannel, respectively; wherein the width of the electrical potentialwell is defined by the position of the first, second and third metallicstructures and their corresponding electric potentials; and wherein thelength of the electrical potential well is defined by the position ofthe third, fourth and fifth metallic structures and their correspondingelectric potentials; and controlling the third electric potential toadjust quantum charge carrier energy levels in the electrical potentialwell.
 16. The method according to claim 15, wherein the third metallicstructure extends around the vertex.
 17. The method according to claim15, wherein the elongate quantum dot extends around the vertex.
 18. Themethod according to claim 15, wherein the polarity of the first andsecond electric potentials is opposite to the polarity of the thirdelectric potential.
 19. The method according to claim 15, wherein thefirst electric potential is substantially the same as the secondelectric potential.
 20. The method according to claim 15, wherein thefourth electric potential is substantially the same as the fifthelectric potential.